Process of drying clays and similar materials



June '1 1926. 1,587,419

'T. H. RHOADS PROCESS OF DRYING CLAYS AND SIMILAR MATERIALS Filed June 21, 1921 fig. Z.

WET E WET awe DRY BULB pry/30.45 aw 50w 7 /O 6 6 5 6 Mim Patented June 1, 1926.

1 UNITED STATES PATENT OFFICE.

' THOMAS H. anonns, or PHILADELPHIA, PENNSYLVANIA, assmnon To rnoo'ron &

SCHWARTZ, INCORPORATED, OF PHILADELPHIA,

TION OI! PENNSYLVANIA.

PENNSYLVANIA, A CORPORA- PROCESS OF DRYING CLAYS AND SIMILAR MATERIALS.

Application filed June 21, 1921. Serial 1T0. 479,367.

The present invention relates to.a process of drying clay bodies, or similar articles, 1n a new and improved manner.

One of the objects of the present invention is to provide a method of drying, and of the steps comprising the same, which will serve to prevent cracking of the clay articles such dried, so that it will not crack, or strain,

even though'the clay is of a very tender character.

In the prior drying of clay articles it was exceedingly difficult to prevent the cracks, or strains, from appearing in the article, especially when operating with a very tender clay that is likely to crack on the slightest change in temperature before actual drying has taken place. I have found that the cracking, or straining, of the clay articles was. due to improper regulation, both as to temperature and the humidity of the atmosphere within the drying compartment.

I have found that strains and cracks in wet clay articles are caused in two ways: first, by reason of unequal drying on the surface, and, second, by contraction, or expansion, due to a sudden change in the temperature of the drying air. The first cause may be corrected by uniform air circulation, but the correction of the second cause is more difficult. By the present method, I-have found a means of correcting the second cause and for providing a uniform and easily regulated temperature within the drying compartment.

In the accompanying drawing:

' Fig. 1 is a transverse sectional view through a drying apparatus, in which my process can be carried out; and Fig. 2 is a sectional plan view of the drying apparatus shown in'Fig. 1.

Referring to the drawing, 1 is the casing of a drier having longitudinal partitions 2, in which there are circulating openings. 3 is a drying compartment. 4 are heating compartments, in which are-the ,steam coils 5, in the present instance. 6 are circulating fans. 7 are longitudinal tracks on which the cars 8 are mounted. 9 are movable partitions arranged to be rolled out of the path of the cars when the cars are shifted in the drying chamber. 10 are movable doors closing the ends of the chamber. 11 are dry bulb thermometers and 12 are wet bulb thermometers located in the several-divisions of the compartments, as shown in Fig. 2.

The dry bulb thermometer 11 and the wet bulb 12 are preferably of a type operable within the drying compartment 3 and having an indicator situated on the outside of the drier casing 1.

The dry bulb thermometer functions in the usual manner to indicate the general temperature within the drying compartment 3. The wet bulb thermometer 12 functions to indicate the temperature of the drying compartment when the bulb thereof is covered with Water, which is usually applied ,by a wick in contact with the bulb and having its opposite end submerged in water. The temperature thereby indicated is due to the evaporation of the water and registers a temperature somewhat below the dry bulb temperature. a

A knowledge of the wet bulb temperature in the drying compartment is necessary in order that it may be accurately controlled in accordance with the wet bulb temperature of the article being dried, an accurate reading of which is acquired by placing the bulb of the article thermometer directly within a sample of the articles being dried, i. e., in i Through this arrangement of thermometers the general temperature of the drying compartment is accurately indicated an controllable; the humidity of the drying compartment-is likewise indicated by thewet bulb and may be accurately controlled:

and the article wet bulb temperature, or the the temperature of the clay an or the drying'may be completed before the partment to a point in exwss of the rletp t moisture in the interior of the cla to a point in excess of the wet bulb temperature of the clay article by water spraying devices 13, the temperature within the compartment being raised in a gradual manner to the proper point, At this point, the dry bulb temperature of the compartment should be not more than, ten degrees. in excess of the wet bulb tem erature, although, in some instances, in dea ing with certain'clays, it may be above ten degrees. This procedure ma es the body of the clay of a uniform temperature, and makes the outside of the clay slightly drier than is really required.

The articles may now be progressed to the next successive chamber of the drying compartment wherein the excessive heat is removed from the air and this step reduces the dry bulb temperatureand the Wet bulb temperature to the dew point, or to the deee where .noeevaporation will take lace. ince the surface of the cla artic es is dry and evaporation cannot ta e place, the article flows to the surface, makin the ha y of the clay uniform throughout. he wet bulb and the dry bulb temperature of the air is now raised to the oint where the wet bulb temperature of the air is slightly hi her than the dry bulb temperature at a point where evapora tion is permitted at a slow rate. Since, in the rior methods, when operating on tender 0 a the article would crack at the slightest c ange in temperature before any actual drying had taken place, it will be seen that, by the present method, this cracking will be prevented b reason of the fact that the clay article wil have been subjected to a certain amount of drying, and also by reason of the fact that the body of the clay will be uniform throughout. As all evaporation takes place on the surface of the clay, it is found that cracking will sometimes occur on the surface due to dr ing, since the drying causes shrinkage o the clay. I have found that in order to prevent cracking at this point a slower rate of evaporation 1s necessary. This may be regulated by, decreasin the ,difi'erence between the temperature 0 the dry and wet bulbs and by allowing a high wet bulb temperature, which heats the clay while it is in the wet condition and aids, or accelerates, the drying in the later'stages.

The articles may now be progressed to the next successive chamber of the drying com artment and the temperature therein regu ated inacoordance with the amount of moisture it is desired to remove from the articles as the drying process progresses,

for exam Is, in the case of bricks it may bedesire to repressthem after a definite ercentag'e otthe moistureis removed and store the drying of the bricks is completed;

articles are removed from the dryin coinpartment, depending entirely upon t e articles being dried and the remaining steps before their completion.

It will be found that by the use of the present method, the clay article, regardless of its fine .character, will not crack, or strain, and will be in perfect condition when removed from the drying compartment.

While I have illustrated one form of drying apparatus that may be used iii carrying out my improved process, it will be understood that the apparatus may be modified without departing from the essential features of the invention.

I claim: 1. The method of drying ceramic articles, which consists of introducing the articles, in a wet condition, into a drying compartment; raising the wet bulb temperature of the compartment to a point close to the wet bulb tem erature of the article; gradually drying the article by increasing the dry 'bulb temperature; then reducing the dry bulb temperature and the wet bulb temperature approximately to the dew point, to permit a flow of moisture from the interior of the article to the slightly drier surface thereof and a uniform temperature of the article throughout its bulk to ensue; then progressivelyincreasing and maintaining the Wet bulb temperature of the air to and at a point slightly in excess of the article wet bulb temperature and increasing the dry bulb temperature of the air slightly in excess of the Wetbulb temperature thereof, until the desired degree of dryness of the article is obtained. i

2. The method of drying ceramic articles, which consists of introducing the articles, in a wet condition into a drying compartment; raising the wet bulb temperature of the compartment to a point close to the wet bulb temperature of the article; raising the dry bulb temperature of the air to a point not exceeding ten degrees in excess of'the wet bulb tem rature of the air; then reducin the dry ulb temperature and the wet bulb temperature substantially to the dew point; permitting a flow of moisture from the interior to the surface of the articles at the dew point; then rogressively increasing and maintaining t e wet bulb tem erature of the air to and at a point slight y in excess of the wet bulb temperature of the article and progressively increasing and maintaining the dry bulb temperature to and at a point in excess of the wet bulb temperature of the air, until the desired state of dryness of the article is obtained.

3. The method of drying ceramic articles, which consists in introducing the same in a wet condition into a drying com artment, raising the wet bulb temperature 0 the comill) lit

tilt) bulb temperature of the article, raising the dry bulb temperature of theair to a point not exceeding ten degrees in excess of thewet bulb temperature, reducing both the wet bulb and dry bulb temperature of the air to the dew point, and, subsequently, again raising the wet bulb temperature of the air to a point in excess of the wet bulb temperature of the article and raising the dry bulb temperature of the air to a point slightly in excess of the wet bulb temperature.

4;. The method of drying ceramic articles, which consists of placing a thermometer within the body of one of said articles, in

order to procure an accurate reading of the temperature of the interior of the article;

introducing the articles in a wet condition creasing the wet bulb tem erature of the.

compartment to a point slig tly in excess of the article temperature; then progressively increasing and maintaining the dry bulb temperature of the compartment to and at a point in excess of the wet bulb temperature of the compartment.

5. The method of drying ceramic articles, which consists of introducing the wet articles into a drying compartment constituting zones of various temperatures throughout its length; regulating the wet bulb temperature of the zone of the compartment adjacent the' entrance thereof to a point close to the wet bulb temperature of the article; gradually drying the articles by regulating the dry bulb temperature to a point in excess of said wet bulb temperature; progressing the articles through the compartment to a zone wherein the wet bulb temperature and the dry bul'btemperature are reduced to approximately the dew point; through a zone wherein the dew point temperatures are maintained and through a zone wherein the wet bulb temperature is progressively increased and maintained at a point in excess of the article wet bulb temperature and the dry bulb temperature is progressively increased and maintained at a point slightly in excess of the wet bulb temperature of the compartment zone, until the desired de ee of dryness 0f the articles is obtaine at Which the articles are removed from the compartment through the exit thereof.

6. The method of drying ceramic articles which consists in mounting the articles to be dried upon cars, moving the cars slowly through a drying chamber of a drying apparatus, raising the wet bulb temperature of the inlet section of the drier to a point close to the wet bulb temperature of the article, gradually drying the articles by Subjecting them to increased dry bulb temperature while the cars with the articles thereon progress, then subjecting the article to air" in circulation in which the dry bulb temperature and a wet bulb temperature are reduced approximately to the dew point to permit the flow of moisture from the interior of the articles to the surface thereof, and as they still further progress subjecting them to air inwhich the wet bulb temperature is increased to a point slightly in excess of the wet bulb temperature of the article and in which the dry bulb temperature of the air is slightly in excess of the wet bulb temperature until the desireddegree of dryness of the article is attained.

THOMAS H. RHOADS. 

